In any internal combustion engine it is desirable to operate the unit in a manner to minimize the amount of pollutants which are discharged into the air. In the instance of a diesel engine, one of the more objectionable elements which is carried by the exhaust gas stream, comprises minute particles of unburned carbon. These particles are manifested in the hot exhaust gas stream by causing the latter to be highly visible with a decidedly black color.
The problem of diesel exhaust gas has been partially overcome by the provision of suitable exhaust gas filters. In such filters, the hot exhaust gas is passed through a filtering bed which is capable of retaining combustible particulate matter. The particle free gas is then discharged into the atmosphere.
After a period of time however, the combustible particulate matter will accumulate in the filter bed to such an extent as to impair the free flow of gas through the bed. When this occurs, a considerable backpressure will be created within the filter, thereby impairing efficient operation of the engine.
As a necessity toward maintaining the engine in good running condition, combustible particulate matter must be removed from the filter. This is often achieved merely by running the engine in a manner that the exhaust gas as it leaves the engine is at a temperature sufficient to cause ignition of the retained particles. Since these particles are normally unburned carbon, it is only necessary to raise the exhaust gas to a temperature of about 1000.degree. F.
When, however, the engine is running under minimal load conditions, and the exhaust gas is relatively cool at approximately 500.degree. F., the carbon particles will not be ignited. Rather, they will be retained and accumulated in the filter section. To achieve the combusting of retained particles, the exhaust gas temperature must be raised to within the desired particle ignition temperature range.
One method for treating low temperature exhaust gas is by introducing a stream of readily combustible fuel into the exhaust gas stream. The gas/fuel mixture will thereafter be passed into the filter's catalyst bed, wherein ignition of the fuel is prompted. The temperature within the catalyst section, as well as the exhaust gas therein, will thus be raised considerably.
Thereafter, gas passing through the filter bed will be heated to effectuate ignition of the combustible particles within the downstream, particle retaining bed.
Among the more recent fuel injection engine developments adapted for conserving fuel, is a type of engine which is powered to operate under heaviest load and accelerating conditions without burning an excessive amount of fuel. This is achieved by use of a multi-cylinder engine having means communicated therewith for immobilizing one or more of the engine's cylinders in response to a load condition.
For example, in the instance of an 8 cylinder diesel engine, the latter might normally be required to operate on four or six cylinders for the major part of its operating period. Yet, for times when the engine must suddenly accelerate, or is subjected to a load heavier than usual, it is desirable to have greater power output. Under such demands, all cylinders of the engine will operate.
For those circumstances wherein full power is required, all the cylinders will automatically become fully operable. For example, all eight cylinders will receive a fuel charge which is intermixed with incoming air. Thereafter, each of the eight cylinders fires in its normal rotation to afford the engine its maximum power output in response to a load condition.
When on the other hand, the engine is running at a normal speed and under less than maximum power, at least one and preferably an even number of cylinders are immobilized.
The means for immobilizing a cylinder is afforded through use of a valve mechanism which is attached to at least some of the intake and exhaust valves. Thus, said valves can be locked in either the fully open or fully closed position.
When the valves are so locked, and when the fuel charge to the immobilized cylinder is discontinued, the piston will merely reciprocate in its normal manner, without imparting output to the engine drive shaft.
During the period of immobilization, the inoperable cylinder or cylinders will receive only a flow of exhaust gas which passes therethrough with no compression being built up.
The immobilized cylinder will continue to function in such manner until the exhaust gas filter becomes rejuvenated, or until an additional load in the form of a need for quick acceleration or a heavier output torque is imposed on the engine. In either instance, the immobilized cylinders will be caused to become instantly operable, by release of the valves, and fuel injection to all cylinders will be reestablished.
In the present arrangement, means are provided for controlling operation of the engine's respective cylinders which are adapted to be selectively immobilized during the engine operating periods. The intake valves, and optionally the exhaust valves of these respective cylinders, are operably communicated with an engine control mechanism.
As each successive cylinder becomes immobilized by adjusting the valve or valves to a fixed position, fuel flow to the cylinder is discontinued. Thereafter, the exhaust filter bed is purged of carbon particles by injecting a measured amount of fuel into the immobilized cylinder. The fuel is then swept up in the exhaust stream to form a combustible, gas/fuel mixture.
It is therefore an object of the invention to provide a method for operating an engine of the type contemplated which is adapted to function with a selective number of cylinders in a manner to avoid the discharge of undesirable, unburned hydrocarbon into the atmosphere. A further object is to provide a method for operating an engine of the type contemplated, wherein the exhaust gas filter is periodically rejuvenated to incinerate accumulated combustible particles. A still further object of the invention is to provide a method for operating an engine-exhaust gas filter combination of the type herein contemplated, wherein supplementary fuel enters the exhaust gas stream in a manner to be combusted within the exhaust gas filter thereby elevating the temperature of the stream.